cmd: bcb: support various block device interfaces for BCB command

cmd: bcb: support various block device interfaces for BCB command

Currently BCB command-line, C APIs and implementation only
support MMC interface. Extend it to allow various block
device interfaces.

Signed-off-by: Dmitrii Merkurev <[email protected]>
Cc: Eugeniu Rosca <[email protected]>
Cc: Ying-Chun Liu (PaulLiu) <[email protected]>
Cc: Simon Glass <[email protected]>
Cc: Mattijs Korpershoek <[email protected]>
Cc: Sean Anderson <[email protected]>
Cc: Cody Schuffelen <[email protected]>
Tested-by: Mattijs Korpershoek <[email protected]> # on vim3
Reviewed-by: Mattijs Korpershoek <[email protected]>